9. Benefit plans
The Dollar General Corporation 401(k) Savings and Retirement Plan, which became effective on January 1, 1998, is a safe harbor defined contribution plan and is subject to the Employee Retirement and Income Security Act ("ERISA").
A participant's right to claim a distribution of his or her account balance is dependent on the plan, ERISA guidelines and Internal Revenue Service regulations. All active participants are fully vested in all contributions to the 401(k) plan. During 2013, 2012 and 2011, the Company expensed approximately $13.0 million, $11.9 million and $10.9 million, respectively, for matching contributions.
The Company also has a nonqualified supplemental retirement plan ("SERP") and compensation deferral plan ("CDP"), known as the Dollar General Corporation CDP/SERP Plan, for a select group of management and other key employees. The Company incurred compensation expense for these plans of approximately $1.2 million, $1.4 million and $1.7 million in 2013, 2012 and 2011, respectively.
The CDP/SERP Plan assets are invested in accounts selected by the Company's Compensation Committee or its delegate. These investments are classified as trading securities and the associated deferred compensation liability is reflected in the consolidated balance sheets as further discussed in Note 6.